Argon and nitrogen are used in a number of industrial applications, including electronics manufacture and metals fabrication. These gases are conventionally produced using cryogenic air separation methods. The cryogenic separation of air to produce argon and nitrogen is described by H. Springmann in IOMA Broadcaster, pp. 14-18 (Jan-Feb 1983). The process produces a significant amount of oxygen in addition to nitrogen and argon, but is not very efficient when utilized to produce only argon and nitrogen. Since the demand for argon and nitrogen is growing at a rapid rate compared to oxygen, there is considerable interest in efforts to increase the efficiency of the production of argon and nitrogen from air.
U.S. Pat. No. 4,732,580, for example, discloses a two-step process for producing argon and nitrogen from air without concomitant production of oxygen using a combination of low temperature pressure swing adsorption ("PSA") and cryogenic distillation. The PSA step produces a stream containing N.sub.2, Ar and a small amount, typically under 0.1%, of O.sub.2 which is subsequently separated cryogenically to produce high purity nitrogen and crude argon. Although this process produces argon and nitrogen from air, it has a number of disadvantages, notable among which is the high capital cost of the high-purity PSA step. In addition, the sieve specific product is low.
The present invention provides an improved process for argon and nitrogen coproduction that is characterized by an increased yield of both argon and nitrogen with a lower capital cost and lower energy requirements in comparison to known processes.